A very convenient method to watch tunnel traffic is setting the verbosity of OpenVPN to the fifth level. This is simply done with the entry verb 5 in its configuration file. The following output shows an excerpt of OpenVPN's protocol file (as specified in the OpenVPN configuration file):

Fri Dec  9 21:05:15 2005 us=51912 Data Channel Encrypt: Cipher 'AES-256-CBC' initialized
 with 256 bit key
Fri Dec  9 21:05:15 2005 us=51944 Data Channel Encrypt: Using 160 bit message hash 'SHA1'
 for HMAC authentication
Fri Dec  9 21:05:15 2005 us=51962 Data Channel Decrypt: Cipher 'AES-256-CBC' initialized
 with 256 bit key
Fri Dec  9 21:05:15 2005 us=52033 Data Channel Decrypt: Using 160 bit message hash 'SHA1'
 for HMAC authentication
Fri Dec  9 21:05:15 2005 us=131924 Control Channel: TLSv1, cipher TLSv1/SSLv3
 DHE-RSA-AES256-SHA, 2048 bit RSA
WRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWRwrWR
wrWRwrWRwrW...